1. Field of the Invention
The present invention relates to float switches and, more particularly, to dependable, non-fouling mercury-activated float switches.
2. Desciption of the Prior Art
Float switches of numerous configurations have been used for various marine and industrial applications. Such switches typically include a base member having mounted thereon a buoyant arm or float member. Electrical circuit and switch means are associated with the arm or member and are responsive to the angular position thereof, whereby the electrical switch means opens and closes as the angular position varies. Typically, changes in the angular position of the arm or member due to changes in water level cause an electrically conductive ball or fluid, such as mercury, to move between switch ON and switch OFF positions to permit or preclude the flow of current through the electrical circuit means.
Float switches of this nature are commonly used in marine environments and are adapted to interrupt or permit current flow, e.g., to a buoy or a pump in a ship's bilge, in response to changing water level. Unfortunately, float switches used in marine environments often malfunction when the mechanical linkage serving as the fulcrum between the buoyant arm or float member and the base member is restricted or obstructed. Typical arms and floats are mechanically linked to the base member by a variety of devices such as pins, rods, shafts, hinges, clamps and the like. U.S. Pat. No. 3,259,981 is exemplary of such a device wherein a lever arm is pivoted on a shaft-type fulcrum which is rotatable in its mounting means. When marine growth such as barnacles, fish slime or fish scales, various types of oils or other forms of foreign matter deposit on or otherwise cling to or obstruct the mechanical linkage, the fulcrum mechanism becomes restricted and causes the switch to stick. When used with a pump, for example, if the switch sticks in the "on" position the pump will not deactivate and the battery or other power source therefor will be depleted. If the switch sticks in the "off" position, the pump will not activate and damage to or loss of the ship due to high water levels may result. One solution to this problem, disclosed in U.S. Pat. No. 3,440,375 to Wood, utilizes a fixed, rigid clamping means engaging a flexible electrical cable as the fulcrum for pivoting a float type mercury switch between ON and OFF positions at the end of the cable. Although the clamp disclosed in the Wood patent is not readily susceptible of either corrosion or obstructive restriction in its operation, the arrangement is undesirable at best since the rigid clamping means contributes to malfunctions by causing the flexible electrical cable to wear and crack at the fulcrum point.